Orthogonal dipoles are used in many known antennas to provide dual polarization. For example, FIG. 1 is a schematic view of an apparatus 100 with orthogonal dipoles and associated feed systems as known in the art. As seen in FIG. 1, the apparatus 100 can include first and second interlacing members 112, 122. Notches or other cut-outs can be included in each member 112, 122 to facilitate the members 112, 122 sliding together to interlace.
Each member 112, 122 can include a center support structure and a dipole 110 (Dipole A), 120 (Dipole B), respectively. However, it is to be understood that each member 112, 122, including its respective center support structure and dipole 110, 120, can be one integral member. In some embodiments, the members 112, 122 can be mounted to a main printed circuit board (PCB) 130 that functions as a ground plane.
A seen in FIG. 1, a first feed microstrip 116 can be disposed on at least a portion of the center support structure of the first member 112, and a second feed microstrip 126 can be disposed on the center support structure of the second member 122. In some embodiments, the feed microstrips 116, 126 can include tuning elements, such as inductors, capacitors, and transformers.
The first feed microstrip 116 can be associated with the first dipole 110, and the second feed microstrip 126 can be associated with the second dipole 120. As seen in FIG. 1, the first feed microstrip 116 and the first dipole 110 can be in the same plane, for example, a plane parallel to the X-Z plane. Similarly, the second feed microstrip 126 and the second dipole 120 can be in the same plane, for example, a plane parallel to the Y-Z plane.
In the apparatus 100 shown in FIG. 1, if the dipoles 110, 120 have coincident centers and are perfectly orthogonal to one another, no coupling will occur between the dipoles 110, 120 themselves. However, the apparatus 100 will still provide poor isolation characteristics because coupling can occur between each dipole and the orthogonal dipole's feed microstrip. For example, this coupling can occur because the electric field of one dipole is parallel with the electric field of the orthogonal dipole's feed microstrip.
As seen in FIG. 1, the first feed microstrip 116 associated with the first dipole 110 is oriented such that its electric field EA MICROSTRIP is parallel to the electric field for the second dipole 120, EB. Accordingly, coupling occurs between the second dipole 120 and the feed microstrip 116 for the first dipole 110.
The feed microstrip 126 associated with the second dipole 120 is oriented such that its electric field EB MICROSTRIP is parallel to the electric field for the first dipole 110, EA. Accordingly, coupling occurs between the first dipole 110 and the feed microstrip 126 for the second dipole 120.
FIG. 2 is a graphical representation of the isolation achieved by prior art systems, for example, the apparatus 100 shown in FIG. 1. As seen in FIG. 2, the isolation can be relatively poor. However, because inter-port isolation is an important factor in antenna performance, these types of poor isolation characteristics are undesirable.
To improve isolation in known antennas, parasitic structures have been placed near radiating elements. The addition of parasitic structures has somewhat improved isolation because the mutual coupling provided by the parasitic elements can help to cancel a portion of the existing coupling between the two polarizations. However, the use of parasitic elements to improve isolation can have adverse effects on the radiation pattern performance of the antenna. Furthermore, parasitic elements typically provide only modest improvements in isolation, but increase cost.
In view of the above, there is a need for a dual polarized antenna and associated feed system with improved isolation.